The goal of this project is to understand the underlying physiological mechanisms of different involuntary movement disorders. The tools we use include clinical neurophysiological methods such as electroencephalography, electromyography, and transcranial magnetic stimulation and neuroimaging with positron emission tomography and functional magnetic resonance imaging. Currently active projects in the Section include studies of tremor and tic. We are using physiological methods to see if criteria can be defined to make the diagnosis of psychogenic tremor. One test that looks promising is measuring the frequency spectrum of the tremor in one extremity while asking the patient to make movements with specified frequencies in the opposite extremity. We are also collecting information regarding patterns of muscle recruitment, sensory modulation and cortical activity (using EEG) associated with psychogenic movements. Analysis reveals that the preparatory cortical activity (measured by pre-movement potentials) is similar to that preceding voluntary movements. The pattern of stimulus-response was found to be highly variable and inconsistent in patients who had stimulus sensitive myoclonus. Following the observation that a patient with Lafora Body Disease was markedly improved with a ketogenic diet, we are currently engaged in a controlled study of more patients. We have completed a study of magnetic resonance spectroscopy in patients with essential tremor that shows a loss of N-acetyl-aspartate in the cerebellum, increasing evidence that the cerebellum is the damaged structure in the disorder.